1. Field of the Invention
The invention relates to the memories of the central processing units of microcomputers and more particularly to a method and device for the predictive reading of a memory so as to improve the security of the microcomputer against fraud as well as the performance characteristics of the memory by increasing the data output speed.
2. Discussion of the Related Art
Items of data contained in a memory are read by means of addresses or addressing codes that are provided successively to the addressing or selection circuits of the memory by the central processing unit of the microprocessor or microcontroller, each addressing code corresponding to a piece of data that is then processed by the central processing unit according to the instruction being executed. In this mode of addressing and reading the memory, the pieces of data contained in the memory are read as and when the addressing codes arrive, the addressing code of the next piece of data to be processed being provided only after the transfer of the previous piece of data into the central processing unit.
This read mode leads to idle time during reading of the memory and therefore results in a time delay. This time delay is detrimental to the speed of computation of the central processing unit.
In certain applications of microcomputers, to improve security against fraud, for example to prevent the user's access code from being discovered by a fraudulent individual, it would be desirable to complicate the task of this fraudulent individual by ensuring that he cannot discover this access code through the analysis of the addressing codes given by the central processing unit.
In other applications of microcomputers such as in mobile telephones, the user or subscriber has access to various services, the number of which depends on the amount of his or her subscription. To this end, the microcomputer is programmed for all the services, but access to some of them will depend on an access code, for example a code A for the basic services corresponding to a certain number of programs, a code B for the basic services plus a certain number of special services corresponding to other programs, a code C for the basic services plus other services corresponding to yet other programs and so on.
In an application of this kind, it is important that a fraudulent individual should be incapable of discovering the meanings of the codes A, B and C. Knowledge of these codes would place him in a position to subscribe only to the basic services (code A) which are the least expensive ones, and to enjoy the additional services of the codes B and C which are the costliest services.